Page 137 - DCAP404 _Object Oriented Programming

Object-oriented Programming

Notes 6.7 Constructor/ Destructor with Static Members

A CLR type, such as a class or struct, can have a static constructor, which can be used to initialize
static data members. A static constructor will be called at most once, and will be called before the
first time a static member of the type is accessed.
An instance constructor will always run after a static constructor.
The compiler cannot inline a call to a constructor if the class has a static constructor. The compiler
cannot inline a call to any member function if the class is a value type, has a static constructor,
and does not have an instance constructor. The common language runtime may inline the call,
but the compiler cannot.
A static constructor should be defined as a private member function, as the static constructor is
only meant to be called by the common language runtime.
To get the equivalent of a static constructor, you need to write a separate ordinary class to hold
the static data and then make a static instance of that ordinary class.

class StaticStuff
{
std::vector<char> letters_;
public:
StaticStuff()
{
for (char c = ‘a’; c <= ‘z’; c++)
letters_.push_back(c);
}
// provide some way to get at letters_
};
class Elsewhere
{
static StaticStuff staticStuff; // constructor runs once, single instance
};

Example:
class A {

int a;
public:
A(int i) {a=i;}
~A() {cout << “bye\n”;}
};
A x(3); // Static constructor
main() {

// do stuff..

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